content: /*
   * Copyright (c) 2009 Andrejs Jermakovics.
   * 
   * All rights reserved. This program and the accompanying materials
   * are made available under the terms of the Eclipse Public License v1.0
   * which accompanies this distribution, and is available at
   * http://www.eclipse.org/legal/epl-v10.html
   *
   * Contributors:
   *     Andrejs Jermakovics - initial implementation
   */
  package it.unibz.instasearch.indexing.querying;
  
  import it.unibz.instasearch.indexing.Field;
  
  import org.apache.lucene.search.BooleanClause;
  import org.apache.lucene.search.BooleanQuery;
  import org.apache.lucene.search.PhraseQuery;
  import org.apache.lucene.search.TermQuery;
  import org.apache.lucene.search.BooleanClause.Occur;
  
  /**
   * Converts a boolean query into a phrase query
   */
  public class PhraseSearcher extends QueryVisitor 
  {
  	/**
  	 * 
  	 */
  	private static final int DEFAULT_SLOP = 10;
  
  	@Override
  	public BooleanQuery visit(BooleanQuery boolQuery) 
  	{
  		PhraseQuery phraseQuery = new PhraseQuery();
  		
  		for(BooleanClause clause: boolQuery.getClauses())
  		{
  			if( clause.isProhibited() || !clause.isRequired() || !(clause.getQuery() instanceof TermQuery) )
  				return super.visit(boolQuery); // only consider required terms
  			
  			TermQuery tq = (TermQuery) clause.getQuery();
  			
  			Field field = Field.getByName( tq.getTerm().field() );
  			if( field != Field.CONTENTS )
  				continue;
  			
  			phraseQuery.add(tq.getTerm());
  		}
  		
  		phraseQuery.setSlop(DEFAULT_SLOP);
  		
  		BooleanQuery bq = new BooleanQuery();
  		bq.add(phraseQuery, Occur.SHOULD);
  		bq.add(boolQuery, Occur.SHOULD);
  		bq.setBoost(boolQuery.getBoost());
  		
  		phraseQuery.setBoost(boolQuery.getBoost());
  		boolQuery.setBoost( phraseQuery.getBoost()*0.5f );
  		
  		return bq;
  	}
  	
  }
  